Composite structural members such as panels made from composite materials are commonly used to form strong, yet lightweight structures. In their simplest forms, composite structural members comprise a number of fibers made of a high tensile and compressive strength material such as glass or carbon, encased within a suitable resinous material. Generally, a number of resin and fiber layers are required to provide a desired strength. More complex composite structural members include a core material sandwiched between sheets of material which may or may not be composites themselves. A "composite structure" for the purposes of this application, is a structure formed by joining two or more separate composite structural members.
Numerous structures are made up of a series of lightweight generally planar panel members that are joined together, usually along their edges. Since the panel members are thin and lightweight, they are not suited to withstand certain types of loads by themselves, compressive and tensile loads for example. Therefore, structures utilizing thin panel members often require other load bearing structural members for taking types of loads on the particular structure that the panel members are unable to withstand alone. A structure comprising a series of panel members and other load bearing members commonly takes advantage of the strengths of each type of member with regard to particular types of loads to produce a strong, yet lightweight structure.
A convenient example of such a structure is a semitrailer adapted for towing behind a truck tractor. Semitrailers are commonly made up of a thin roof panel, thin wall panels, and a somewhat heavier reinforced floor panel, connected together along the edges with corner members to form a box-like structure. Such a semitrailer structure is in the nature of a box beam in which the flat panels take shear loads, and the corner members take compressive and tensile loads.
Prior semitrailers have commonly been made of noncomposite steel or aluminum panels that have been either rivetted or welded into an extrusion that formed the corners of the trailer box. This type of semitrailer body had a number of drawbacks. First, the structure required extensive riveting or welding in the panel joint areas, both of which made fabrication more expensive. Furthermore, a jig was required to position the various parts for joining. Also, the extrusion corner members had to have a relatively large cross-section in order to withstand the loads placed upon them, but were connected directly to the relatively thin panel members. The abrupt change in section made the joint subject to fatigue, and provided a stress riser in the structure. Furthermore, the structure had to be nearly square, thereby becoming an undesirable configuration with regard to both stress and aerodynamics.
Box beam structures such as the semitrailer example, have also been made from composite panel members. In the case of composite panel members, the panels were joined together by separate corner members that were not necessarily made of composite materials themselves. Similarly to the conventional metal panels, the composite panels took shear loads while the separately formed corner members took compressive and tensile loads. Structures comprised of composite panels and separate corner members suffered from problems similar to those associated with conventional metal trailer structures.
It is therefore an object of the invention to provide a composite structural member having an integrally formed composite joint-forming edge structure that can be bonded to a complementing joint-forming edge structure of another composite structural member to form a joint structure that is capable of withstanding types of loads that the composite structural members cannot withstand by themselves.
A further object of the invention is to provide a method for making a composite structural member with an integral joint- forming edge structure that, when bonded to a complementing joint-forming edge structure of another composite structural member, forms a load-bearing structure for taking loads that the composite structural members alone are incapable of withstanding.
Another object of the invention is to provide a method for joining composite structural members having complementing joint-forming edge structures.